Method and apparatus for monitoring tire performance

ABSTRACT

A method and apparatus for assessing tire performance by generating accurate, timely tire-to-surface slippage information under any operational/environmental conditions and on any road and/or off-road surface without requiring instrumentation of the roadway. The approach is capable of storing generated tire-to-surface slippage information for later retrieval and analysis and/or capable of supporting dynamic, real-time collection and dissemination of generated data. One exemplary embodiment generates and disseminates tire-to-surface slippage information in real-time that is compatible with and may be formatted for use by any consumer vehicle control system as well as external test and analysis equipment.

This is a Division of application Ser. No. 11/030,813 filed Jan. 7, 2005now U.S. Pat. No. 7,114,383. The disclosure of the prior application ishereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention pertains to vehicle tire performance monitoring.In particular, the present invention pertains to monitoring slippagebetween a vehicle tire and a road or off-road surface.

2. Description of Related Art

Slippage between the tread blocks of a vehicle's tires and the surfaceupon which the vehicle is operating greatly affects overall tire andvehicle performance. For example, slippage of a tire against a road oroff-road surface typically results in tire tread wear and a reducedoperational life of the tire. Further, slippage of a tire against a roador off-road surface results in a loss of torque generated by the vehicleengine and power train, resulting in less efficient operation of thevehicle. Slippage also results in a loss of vehicle maneuverability inthat a vehicle may fail to hold to the surface upon which the vehicle isoperating, thereby causing the driver to limit the range of operationalmaneuvers performed in the vehicle. In a worst case scenario, slippageof one or more tires against a road or off-road surface can result is aloss of vehicle control which may result in an accident.

Unfortunately, accurate slippage information of a tire upon a roadsurface under a variety of operational and environmental conditions has,traditionally, been very difficult to obtain. One conventional approachis to place instruments within a test road surface itself. For example,one approach is to install within a test road surface a steel plate witha hole in the steel plate through which an instrumented needle protrudesabove the surface of the plate. A test vehicle is driven along the testroad surface and over the steel plate containing the instrumentedneedle. As a tire on the vehicle contacts the needle, the needle movesin the direction of slippage. A measure of the slippage may thereby berecorded by the needle's instrumentation.

One drawback associated with such an approach is that you can onlycollect data on a single point on the road surface and not on the tireitself. Therefore, although information is collected, it is unknownwhether the information collected relates to a point at the front of thetire footprint or the back of the tire footprint. Such a drawback may bemitigated by using a plate that includes a matrix of instrumentedneedles. Although such an approach provides increased information overthe footprint of the tire, the surface for which the measurements arecollected remain measurements for slippage on the steel plate surfacerather than the actual road surface. Further, it is difficult to usesuch an approach to determine slippage under a wide range of maneuversdue to the need to place one or more plates in a manner that allows themaneuver to be performed while the vehicle is over the steel plates.Still further, such an approach is not effective for measuring slippageunder certain environmental conditions, such as snow, ice, and mud, norcan such an approach be used to measure slippage in off-roadenvironments. In addition, efforts to collect slippage information usingsuch instrumented plate techniques is typically very repetitious andtime consuming. The results generated are often incomplete, error proneand/or ambiguous.

SUMMARY OF THE INVENTION

The need for tire slippage information is widespread. For example, tiremanufacturers need slippage information in order to verify that a set oftires meets original equipment manufacturer (OEM) specificationrequirements when a set of the tires are mounted upon a new vehicle.Further, tire manufacturers need slippage information to assess and tofine-tune the performance of aftermarket as well as OEM lines of tiresfor road and off-road vehicles as well as tires used by heavy equipmentsuch as earth movers and large trucks used in the construction, forestryand mining industries.

Slippage information can also be used to optimize the performance of avehicle/tire combination for a specific set of operating conditions. Forexample, tire slippage information measured for a racing vehicle duringtrial laps on a specific race track may be used to select an optimal setof tires for that racing vehicle on that particular track. Further, suchslippage information can be used to adjust the suspension of the racingvehicle prior to the race in order to minimize slippage at key locationson the race track. Given that in competitive, high-stakes races thedifference between first place and third place may only be a matter ofhundredths of a second, optimizing a vehicle prior to the race to reduceslippage without significantly degrading other performance criteria(e.g., gas mileage, vibration at high speed, handling, etc.) may be thedifference between winning and losing a major race.

Accurate, real-time measurements of actual tire-to-surface slippageinformation would be of great direct benefit to both the tire andvehicle industries as well as the general consumer population. Consumerpassenger vehicles currently employ computerized control modules thatallow the performance of the vehicle to be controlled, altered oroptimized. Engine control systems and anti-lock breaking systems arecommon in today's vehicle's. Such control modules often communicate withand receive command and control information from a vehicle controlmanagement system that is responsible for the integration of thefunctions performed by each of the respective control systems. Stabilitycontrol systems have recently been introduced that assist in maintainingvehicle stability under difficult driving conditions. Although suchcontrol systems would benefit greatly from accurate, real-timemeasurements of actual tire-to-surface slippage information, suchinformation is not currently available for their use. As a result, thecabilities of such systems are often limited with respect to the levelof optimization that can be achieved.

Hence, a need remains for a method and apparatus for collecting anddisseminating accurate measurements of tire-to-surface slippageinformation. The approach should support the collection of accurate,timely tire-to-surface slippage information under anyoperational/environmental condition and on any road and/or off-roadsurface without requiring instrumentation of the roadway. The approachshould be capable of storing generated tire-to-surface slippageinformation for later retrieval and analysis and/or should be capable ofdynamic, real-time collection and dissemination of generated data.Preferably the approach would generate tire-to-surface slippageinformation in real-time that is compatible with and may be dynamicallyformatted for use by consumer vehicle control systems as well asexternal test and analysis equipment.

An exemplary embodiment of the present invention provides a method andapparatus for generating accurate, timely tire-to-surface slippageinformation under any operational/environmental condition and on anyroad and/or off-road surface without requiring instrumentation of theroadway. The approach is capable of storing generated tire-to-surfaceslippage information for later retrieval and analysis and is capable ofsupporting dynamic, real-time collection and dissemination of generateddata. One exemplary embodiment generates and disseminatestire-to-surface slippage information in real-time that is compatiblewith and may be dynamically formatted for use by any consumer vehiclecontrol system as well as external test and analysis equipment.

In a first exemplary embodiment of the invention, a method formonitoring slippage of a tire contact area against a surface isdescribed that includes generating a reference frame of the surface incontact with a portion of the tire contact area, generating a sampleframe of the surface in contact with the portion of the tire contactarea and comparing the reference frame with the sample frame todetermine whether the portion of the tire contact area has movedrelative to the surface.

In a second exemplary embodiment of the invention, an apparatus isdescribed for monitoring slippage of a tire contact area against asurface that includes a sensor module that generates a reference frameof the surface in contact with a portion of the tire contact area andsubsequently generates a sample frame of the surface in contact with theportion of the tire contact area and a processor module that comparesthe reference frame with the sample frame to determine whether theportion of the tire contact area has moved relative to the surface.

In a third exemplary embodiment of the invention, a program productapparatus is described having a computer readable medium with computerprogram logic recorded thereon for monitoring slippage of a tire contactarea against a surface that includes a sensor module that generates areference frame of the surface in contact with a portion of the tirecontact area and subsequently generates a sample frame of the surface incontact with the portion of the tire contact area and a processor modulethat compares the reference frame with the sample frame to determinewhether the portion of the tire contact area has moved relative to thesurface.

In a fourth exemplary embodiment of the invention, a method fordetermining an amount of wear of a tire tread is described that includesrecording a first signal propagation time for a signal to travel along apath that includes a distance from the bottom of a tire groove to asurface in contact with the tire tread, recording a second signalpropagation time for a signal to travel along a path that includes adistance from the bottom of the tire groove to a surface in contact withthe tire tread and determining the amount of wear of the tire treadbased upon a comparison of the first propagation time with the secondpropagation time.

The above features and advantages of the present invention will becomeapparent upon consideration of the following descriptions anddescriptive figures of specific exemplary embodiments thereof. Whilethese descriptions go into specific details of the invention, it shouldbe understood that variations may and do exist and would be apparent tothose skilled in the art based on the descriptions herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a front, or tread, view of an automobiletire that has been equipped with slippage monitoring sensors inaccordance with an exemplary embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views of an automobile tire that hasbeen equipped with slippage monitoring sensors in accordance with afirst exemplary embodiment of the present invention.

FIG. 3 is a cross-sectional view of an automobile tire and wheel rimthat has been equipped with slippage monitoring sensors in accordancewith a second exemplary embodiment of the present invention.

FIG. 4 is a modular block diagram of a slippage monitoring module inaccordance with an exemplary embodiment of the present invention.

FIG. 5 is a process flow diagram describing a process used by a slippagemonitoring module to generate correlation values based upon outputreceived from a slippage monitoring sensor in accordance with anexemplary embodiment of the present invention.

FIG. 6 is a diagrammatic representation of the correlation process flowdescribed in FIG. 5.

FIG. 7 is a schematic view of a slippage monitoring sensor module inaccordance with an exemplary embodiment of the present invention.

FIG. 8 is a modular block diagram of a slippage monitoring controlmodule in accordance with an exemplary embodiment of the presentinvention.

FIG. 9 is a process flow diagram describing a process used by a slippagemonitoring control module to determine an amount of tire/vehicleslippage in accordance with an exemplary embodiment of the presentinvention.

FIG. 10 is a modular block diagram of a vehicle control managementsystem with integrated slippage monitoring in accordance with anexemplary embodiment of the present invention.

FIG. 11 is a process flow diagram describing a process used by a vehiclecontrol management system with integrated slippage monitoring tooptimize vehicle performance using tire-to-surface slippage informationin accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments according to the present invention are describedbelow with reference to the above drawings, in which like referencenumerals designate like components.

Exemplary embodiments of the present invention relate to a novel methodand apparatus for generating and disseminating tire-to-surface slippageinformation.

FIG. 1 presents a perspective view of a front, or tread, view of anautomobile tire that has been equipped with slippage monitoring sensors.As shown in FIG. 1, tire 100 may include a plurality of tire treadsurfaces 102 separated by tire tread groves 104. As further shown inFIG. 1, a plurality of slippage monitoring sensor optical fibers 106 maybe mounted from within the tire so that the tip of an optical fiberassociated with each slippage monitoring sensor 106 is flush with asurface of one or more of tire tread groves 104.

Placement of slippage monitoring sensor optical fibers 106 within tiretread groves protects the slippage monitoring sensor optical fibers fromdamage due to contact with the road surface. Although dirt maytemporarily fill a tire grove, tires are typically designed so thatdebris does not stay permanently lodged in the tire groves.

Sensor optical fibers 106 may be placed anywhere within tire 100 in anynumber and density. For example, one or more slippage monitoring sensoroptical fibers 106 may be placed within a selected tire grove, or acrossmultiple tire groves. The slippage monitoring sensor optical fibers 106may be placed along the entire periphery of the tire or within a portionof the tire periphery. Sensor optical fibers 106 may also be placedwithin one or more tread blocks of tire tread surfaces 102, slightlyrecessed from the outer surface of the tread blocks. Such placement maybe useful for assessing tire performance under controlled developmentand/or test conditions in which the surface is free of debris which mayotherwise block the view of the sensor optical fibers 106.

FIG. 2A is a cross-sectional views of an automobile tire that has beenequipped with slippage monitoring sensors in accordance with anexemplary first embodiment. As shown in FIG. 2A, tire 200 may include aplurality of tire tread surfaces 202 separated by tire tread groves 204.As further shown in FIG. 2A, a plurality of slippage monitoring sensoroptical fibers 206 may be mounted from within the tire so that the tipof optical fibers associated with each slippage monitoring sensor 206 isflush with a surface of one or more tire tread groves 204.

As further shown in FIG. 2A, one or more slippage monitoring sensoroptical fibers 206 may be fed into a slippage monitoring module 208 thatis mounted to the interior surface 212 of tire 200 by a strong andflexible cushion of adhesive 210 (such as a silicon based adhesive).Although not shown in FIG. 2A, slippage monitoring sensor optical fibers206 may also be cushioned by and adhered to interior surface 212 of tire200 by a strong and flexible cushion of adhesive 210. In this manner,both slippage monitoring module 208 and the one or more slippagemonitoring sensor optical fibers 206 may be protected from damage due tocentrifugal forces generated by rotation of tire 200. The flexiblecushion formed by adhesive 210 also protects slippage monitoring module208 and the one or more slippage monitoring sensor optical fibers 206from forces due to flexing of tire 200 in response to uneven road andoff-road surfaces while the tire is in operational use.

FIG. 2B is a cross-sectional view of the tire presented in FIG. 2A alongthe line marked 2B. As shown in FIG. 2B, slippage monitoring module 208may be cushioned by flexible cushion of adhesive 210. Further, slippagemonitoring sensor optical fibers 206 may enter slippage monitoringmodule 208 close to the interior tire surface 212, thereby providingslippage monitoring sensor optical fibers 206 with maximum structuralsupport from flexible cushion of adhesive 210 and interior surface 212to minimize damage to slippage monitoring sensor optical fibers 206 dueto centrifugal forces and forces due to tire impacts with road surfaces.

FIG. 3 is a cross-sectional view of an automobile tire 300 and the outersurface of a wheel rim 320 exposed by removing half of tire 300. Asshown in FIG. 3, tire 300 may include a plurality of tire tread surfaces302 separated by tire tread groves 304. As further shown in FIG. 3, aplurality of slippage monitoring sensor optical fibers 306 may bemounted from within the tire so that the tip of an optical fiberassociated with each slippage monitoring sensor 306 is flush with asurface of one or more of tire tread groves 304. One or more slippagemonitoring modules 308 may mounted to the outer surface of wheel rim 320by a strap 310. Strap 310 may be made of any material sufficientlyresistant to stretching and loosening as a result of centrifugal forcesapplied to the strap and one or more slippage monitoring modules 308 asa result of operational use of the wheel and tire.

Slippage monitoring sensor optical fibers 306 may be structurallysupported against centrifugal forces and impact forces by a structuralsheath 314. Each structural sheath 314 may adhere to interior surface312 of tire 300 around a slippage monitoring sensor optical fiber 306and further may adhere to the exterior and/or interior surface of aconnector clip 310 that fastens to the top of slippage monitoring module308, thereby connecting one or more slippage monitoring sensor opticalfibers 306 to the top of slippage monitoring module 308.

As described above, strap 310 may be used to hold one or more slippagemonitoring modules 308 to the exterior of wheel rim 320 and eachslippage monitoring module 308 may support one or more slippagemonitoring sensor optical fibers 306. These fibers may be configured toattach to automobile tire 300 at any point in order to collecttire-to-surface slippage information at the specific location selected.

FIG. 4 presents a block diagram of an exemplary embodiment of a slippagemonitoring module 400 that supports collection of tire-to-surfaceslippage information. As shown in FIG. 4, slippage monitoring module 400may include a controller/processor module 402 in communication with oneor more slippage monitoring sensor modules 404. Slippage monitoringmodule 400 may further include a storage module 406, a transmittermodule 408, and a receiver module 410. Each of these modules maycommunicate with storage module 406, either directly or viacontroller/processor module 402.

As described in greater detail with respect to FIG. 7, below, eachslippage monitoring sensor module 404 is capable of illuminating andcapturing images of a portion of a road or off-road surface within thefootprint of a tire. As described in greater detail with respect to FIG.5, below, controller/processor module 402 controls each slippagemonitoring sensor module 404 within monitoring module 400 to generatereference and sample images. Controller/processor module 402 furtherperforms correlation processing to determine the degree of change in theimages. The generated correlation information may be used to determinewhether slippage has occurred and may be used to determine the magnitudeand direction of the slippage, if slippage has occurred.

In one exemplary embodiment, controller/processor module 402 may storegenerated correlation data and/or slippage information in storage module406. Stored correlation data and/or slippage information may remain instorage module 406 until a user requests transfer of the data to anexternal analysis system. In such an exemplary embodiment,controller/processor module 402 may receive a request for an upload ofdata from an external analysis system via receiver module 410. Inresponse, controller/processor module 402 may retrieve the requesteddata from storage module 406 and transmit the retrieved information tothe external analysis system via transmitter module 408. Time stamps, orsequence information, included in the correlation data and/or slippageinformation may allow the external analysis system to observe andanalyze the data in a meaningful manner and/or to correlate thegenerated slippage information with information collected simultaneouslyby other vehicle sensors.

In another exemplary embodiment, controller/processor module 402 maydynamically transmit correlation data and/or slippage information inreal-time or near-real-time to an external analysis system locatedwithin the vehicle or within transmitter broadcast range of the vehicle.Controller/processor module 402 may dynamically transmit correlationdata and/or slippage information in real-time or near-real-time to aslippage monitoring control module mounted within the chassis of thevehicle. The slippage monitoring control module may further process thereceived slippage information and may coordinate with other vehiclecontrol modules in an integrated manner, as described below with respectto FIG. 10.

Controller/processor module 402 may control the generation of referenceand sample images and generate correlation and slippage information inany manner. One approach for generating correlation values andinformation related to movement based upon an analysis of reference andsample images is described in U.S. Pat. No. 5,644,139 (or '139 patent)to Allen et al. entitled, “Navigation Technique for Detecting Movementof Navigation Sensors Relative to an Object,” the content of which ishereby incorporated by reference in its entirety. Although the techniquedescribed in the '139 patent is directed to detection of movement of anoptical text scanning device. The same approach may be applied to thedetection of movement of a tire relative to a road or off-road surface.The exemplary approach, as described in the '139 patent is describedbelow with respect to FIGS. 5-7 which are based, in whole or in partupon FIGS. 7 and 8 and FIG. 4 of the '139 patent, respectively.

FIG. 5 is a process flow diagram describing a process used by a slippagemonitoring module to generate correlation values based upon outputreceived from a slippage monitoring sensor. As shown in FIG. 5, at stepS502, controller/processor module 402 (FIG. 4) may instruct a slippagemonitoring sensor module 404 to generate and store in storage module 406a reference image, or reference frame, of the road or off-road surfacebeneath a slippage monitoring sensor optical fiber connected to slippagemonitoring sensor module 404. Next, at step S504, controller/processormodule 402 may instruct slippage monitoring sensor modules 404 togenerate and store in storage module 406 a sample image, or sampleframe, of the road or off-road surface. A sample frame is generated inthe same manner as a reference frame, but is taken at a later time.

Once a sample frame has been generated controller/processor module 402may perform correlation computations, at step S506, as described ingreater detail below, to determine a level of correlation between thereference frame and the sample frame. During the correlation process,controller/processor module 402 may compare the image captured in thereference frame and the image captured in the sample frame to determinethe amount of slippage, if any, that may have occurred during the timeperiod between the frames. The time interval between the reference frameand the first sample frame, and between each subsequent sample frame andthe previous sample frame, may be such that the same image is present ineach frame, thus allowing correlation to be successful. The timeinterval between frames may be pre-set and/or dynamically set so that afeature within a captured image shifts by no more than a single pixelbetween frames.

If, at steps 506, the correlated images are found to have shifted by asingle pixel or less, controller/processor module may determine, at stepS508, that a microstep has occurred and the reference frame is shifted,at step 516, by a determined correlation difference and processing mayproceed with step S504 and the acquisition of a new sample frame. If,however, at steps 506, the correlated images are found to have shiftedby more than a single pixel, controller/processor module may determine,at step S508, that a shift in the image greater than a microstep hasoccurred and the sample frame may be made the new reference frame, atstep S510.

If the controller/processor module determines, at step S512, that thecorrelation was successful, processing may proceed to step S504 and theacquisition of a new sample frame, otherwise, the controller/processormodule may increase the frame sampling interval, at step S514. In such acase, processing may proceed to step S502 and the acquisition of a newreference frame.

FIG. 6 is a diagrammatic representation of one exemplary embodiment ofthe correlation process flow described with respect to FIG. 5.Correlation processing compares the positions of inherent structuralfeatures captured in successive frames to provide information related tothe position of a slippage monitoring sensor optical fiber relative toan initial position represented by a reference frame image.

The processing of FIG. 6 is typically performed for each slippagemonitoring sensor optical fiber. While the correlation processing isperformed computationally, the concepts of this exemplary embodiment maybe described diagrammatically. As shown in FIG. 6, a reference frame 602is shown as having an image of a T-shaped inherent structural feature604. The size of the reference frame depends upon factors such as themaximum processing speeds of the sensor and controller/processordevices, the dominant spatial frequencies in the imaging of thestructural features, and the image resolution of the sensor. Forexample, a reference frame that is 24 by 56 pixels in size may be usedin association with an image sensor or CCD that creates a thirty-twopixel (N) by sixty-four pixel (M) image.

At a later time (dt) the controller/processor module will instruct theslippage monitoring sensor module sample frame 606. If tire-to-surfaceslippage has occurred during the period between generate images, sampleframe 606 may be displaced with respect to frame 602, but showsubstantially the same inherent structural features. The duration dt maybe set such that the relative displacement of the inherent structuralfeatures is less than one pixel of the slippage monitoring sensoroptical fiber.

If tire-to-surface slippage has occurred during the time period betweenacquiring the reference frame 602 and acquiring the sample frame 606,the first and second images of the inherent structural features will beones in which the feature has shifted. While the exemplary embodiment isone in which dt is less than the time that allows a full-pixel movement,the schematic representation of FIG. 6 is one in which therepresentative feature 604 is allowed to shift up and to the right byone pixel. The full-pixel shift is assumed only to simplify therepresentation.

Element 610 in FIG. 8 represents a sequential shifting of the pixelvalues of frame 608 into the eight nearest-neighbor pixels. That is,step “0” does not include a shift, step “1” is a diagonal shift upwardand to the left, step “2” is an upward shift, etc. In this manner, thepixel-shifted frames can be combined with the sample frame 606 toproduce the array 612 of position frames. The position frame designatedas “Position 0” does not include a shift, so that the result is merely acombination of frames 606 and 608. “Position 3” has the minimum numberof shaded pixels, and therefore is the frame with the highestcorrelation. Based upon the correlation results, the position of theT-shaped feature 604 in the sample frame 606 is determined to be adiagonal rightward and upward shift relative to the position of the samefeature in earlier-acquired reference frame 62, which implies that thetire has slipped leftwardly and downwardly during time dt.

While other correlation approaches may be employed, an acceptableapproach is a “sum of the squared differences” correlation. For theexemplary embodiment of FIG. 6, there are nine correlation coefficients(C_(k)=C₀, C₁. . . C₈) formed from the nine offsets at element 610, withthe correlation coefficients being determined by equation:C _(k)=Σ_(i)Σ_(j)(S _(ij) −R _((ij)+k))²where S_(ij) denotes the slippage monitoring sensor module measuredvalue at the position ij of the sample frame 606 and R_(ij) denotes theslippage monitoring sensor module measured value at the frame 608 asshifted at the element 610 in the k direction, with k being theidentifier of the shift at element 610. In FIG. 6, k=3 provides thecorrelation coefficient with the lowest value.

Correlations are used to find the locations of identical features insuccessive frames in order to determine the displacements of thefeatures from frame-to-frame. Summing or integrating these displacementsand correcting for scale factors introduced through the design of therelevant optics determine the tire-to-surface slippage displacementsduring the slippage monitoring process.

As previously noted, the frame-to-frame correlations may be referred toas “microsteps,” since frame rates are chosen to be sufficiently high toensure that the displacements do not exceed the dimension of a singlepixel. Oversampling can provide sub-pixel displacement precision.Referring to FIG. 5, a determination at step S508 that a microstep is tobe taken is made following each computation at step S506 of thecorrelations. If a microstep is required, the reference frame is shiftedat step S516. In this step, the sample frame 606 of FIG. 6 becomes thereference frame and a new sample frame is acquired. The correlationcomputation is then repeated.

While the process provides a high degree of correlation match, anyerrors that do occur will accumulate with each successive shift, at stepS516, of a sample frame 606 to the reference frame designation. In orderto place a restriction on the growth rate of this “random walk” error, asample frame may be stored in a separate buffer memory. This separatelystored sample frame becomes a new reference frame for a subsequentseries of correlation computations. The latter correlation may bereferred to as a “macrostep.”

By using macrosteps, a more precise determination of slippage monitoringsensor optical fiber displacement across a distance of m image framedisplacements, i.e. m microsteps, can be obtained. The error in onemacrostep is a result of a single correlation calculation, whereas theequivalent error of m microsteps is m^(1/2) times the error in a singlemicrostep. Although the average of errors in m microsteps approacheszero as m increases, the standard deviation in the average of errorsgrows as m^(1/2). Thus, it is advantageous to reduce the standarddeviation of accumulated error by using macrosteps having m as large aspractical, as long as the two frames that define a macrostep are not sofar spaced from one another that they have no significant region ofcommon image content.

As described in FIG. 5 with respect to step S514, the sampling period dtdoes not have to be constant. The sampling period may be determined as afunction of previous measurements. One method that employs a variable dtis to improve the accuracy of displacement calculation by keeping therelative displacement between successive reference frames within certainbounds. For example, the upper bound may be one-pixel displacement,while the lower bound is determined by numerical round-offconsiderations in the processing of the correlation data.

FIG. 7 is a schematic view of a slippage monitoring sensor module 700 asdescribed in FIG. 4 with respect to block 404. As shown in FIG. 7, lightfrom a source 722 is collimated at illumination optics 724 and thenredirected by an amplitude splitting beam-splitter 726 and focused bylens 727 for transmission via slippage monitoring sensor optical fiber706 to illuminate a portion of the road surface 740 in contact with anoutside surface 742 of a tire. A portion of the light energy from theLED direct to and transmitted through the beam-splitter is not shown inFIG. 7. The light energy from the beam-splitter illuminates the roadsurface 740 at a normal angle.

Also represented in FIG. 7 is the portion of the light energy that isreflected or scattered from road surface 740 and passed via slippagemonitoring sensor optical fiber 706 through focusing lens 727 to thebeam-splitter 726 for filtering at element 728 and focusing via element730 to form an image upon imaging device 732 (e.g., a CCD). The portionof light energy passing from the road surface to the beam-splitter andreflecting from the beam-splitter is not shown. The magnification ofcorrelation imaging optics should be constant over the field-of-view ofthe two-dimensional imaging device 732 which detects the focused light.Further, the optics should be configured so that the road surface imageremains in focus despite significant wear to the outside tread of thetire. Alternately, the optics should be capable of being periodicallyand/or dynamically re-focusing to accommodate tire tread wear.

Slippage monitoring sensor module 700 may also be configured to workwith the slippage monitoring module (see FIG. 4) to determine the amountof tread wear that has occurred on the tire tread. In one exemplaryembodiment, slippage monitoring sensor module 700 records at sensorarray 732 a time of arrival of light emitted by light source 722 andreflected off road surface 742 prior to detection at imaging device 732.By comparing the time of arrival to a time at which a pulse of light wasinitiated, a total propagation time may be determined. By comparing arecently measured total propagation time with a previously measured andstored total propagation time, a change in the total propagation timemay be determined that excludes delays introduced by the respectivehardware components. This determined change in propagation time may thenbe used to determine a change in the overall distance that the light hasbeen propagated between the two different measurements. This change inpropagation distance equates to the wear in the tread of the tire sincethe stored measurement was made.

By comparing the determined measure of tire tread wear with a previouslystored tread depth value received from an external system or apreviously measured tread depth measured by a user and stored in memory,slippage monitoring sensor module 700 may determine the depth of thetread remaining on the tire. In one exemplary embodiment, slippagemonitoring sensor module 700 is configured via communication with anexternal module (e.g., the slippage monitoring control module) with theinformation needed to periodically determine the depth of treadremaining on the tire and to report to the external module when one ormore predetermined tired tread thresholds have been exceeded. It shouldbe noted that light source 722 may emit infrared light but could bemodified to emit any light frequency. Further, it should be noted thatunless a surface is in contact with the tired tread opposite a slippagemonitoring sensor optical fiber, no reflection can occur and no framewith information related to the surface can be generated. Slippagemonitoring sensor module may be configured to only generate frames whenreflected light above a pre-selected or dynamically selected thresholdis detected. Such an approach may be used to assure that frames aregenerated only for slippage monitoring sensor optical fibers within atire footprint in contact with a surface.

FIG. 8 presents a block diagram of an exemplary embodiment of a slippagemonitoring control module 800 that communicates with one or moreslippage monitoring modules (FIG. 4) to disseminate control informationto the respective slippage monitoring modules and to process anddisseminate tire-to-surface slippage information received from therespective slippage monitoring modules.

As shown in FIG. 8, slippage monitoring control module 800 may include acontroller/processor module 802, a storage module 806, a transmittermodule 808, a receiver module 810 and an external interface module 812.

In one exemplary embodiment, slippage monitoring control module 800receives via receiver module 810 correlation information from one ormore slippage monitoring modules, each supporting one or more slippagemonitoring sensor modules. In such an exemplary embodiment,controller/processor module 802 may process information received withrespect to each slippage monitoring sensor module to determine thedistance and direction (e.g., in terms of ΔX and ΔY coordinates) of adetected slippage. Controller/processor module 802 may further processthe information received from the slippage monitoring sensor modules todetermine which tires are slipping and the direction in which each tireis slipping. Depending upon the severity of the slipping detected,controller/processor module 802 may identify an alert condition thatcorresponds to a corrective action that may be initiated to correct theslippage and a magnitude of the correction needed.

Controller/processor module 802 may store the slippage informationreceived and/or generated in storage module 806. Further,controller/processor module 802 may forward, via external interfacemodule 812 received and/or generated slippage information and/orgenerated alerts to an external analysis system and/or to one or moreexternal vehicle control modules capable of implementing correctiveaction. As shown in FIG. 8, slippage monitoring control module 800 iscapable of interfacing with a standard external analysis system.Further, as shown in FIG. 8, slippage monitoring control module 800 iscapable of interfacing with a vehicle control management system, anengine control system, a breaking control system and a stability controlsystem. Each of these respective external modules may be configured toreceive tire-to-surface slippage information and alerts generated byslippage monitoring control module 800 and to implement correctiveaction.

As further shown in FIG. 8, slippage monitoring control module 800 mayreceive information from external systems. This received information mayinclude control parameters and/or configuration data that controls howslippage monitoring control module 800 is to communicate with therespective external devices (e.g., periodically, in real-time, on analert-only basis, etc.) and the information that each external moduleexpects to receive (e.g., slippage measurements per tire, alert codeswith severity indicators, etc.). The received information may alsoinclude configuration and command/control instructions used by theslippage monitoring control module 800 to manage the respective slippagemonitoring modules and to manage in information generated by therespective slippage monitoring modules. For example, in one exemplaryembodiment, vehicle speed information received from a vehicle controlmanagement system may be used to determine an initial frame samplingrate used by the respective slippage monitoring modules. Informationreceived from external systems may be dynamically or statically storedin storage module 806. In this manner the configuration informationreceived from external systems may remain either temporarily orpermanently available for use in configuring/controlling slippagemonitoring control module 800 operation and the manner in which slippagemonitoring control module 800 communicates with external systems.

FIG. 9 is a process flow diagram describing a process used by a slippagemonitoring control module 800 (FIG. 8) to determine and report an amountof tire/vehicle slippage. As shown in FIG. 9, after startup of avehicle, at step S902, the slippage monitoring control module mayreceive correlation values from one or more slippage monitoring modules,at step S904. Based upon the received correlation values, the slippagemonitoring control module may determine, at step S906, an amount ofchange in an X direction and an Y direction (i.e., a ΔX/ΔY) for eachslippage monitoring sensor optical fiber location, and may determineadditional qualitative information that characterizes the nature of themeasured slippage for one or more tires. If the slippage monitoringcontrol module determines, at step S908 that a performance threshold hasbeen exceeded, an alert condition may be generated and associated withthe slippage information at step S910. Next, the slippage monitoringcontrol module may report, at step S912, the slippage information and/oralert data to one or more external modules (e.g., a vehicle controlmanagement module, an engine control management system, a breakingcontrol system, stability control system, etc.) so that correctiveaction may be taken based upon the nature of the detected slippageinformation and the corrective capabilities of the vehicle. Upon turningoff the vehicle, at step 914, process flow terminates, otherwiseprocessing continues with the receipt and processing of furthercorrelation values at step S904.

FIG. 10 is a modular block diagram of a vehicle control managementsystem with integrated slippage monitoring. The identified controlsystems depicted in FIG. 10 have been described above in connection withthe slippage monitoring control module. As shown in FIG. 10, a exemplaryvehicle with sophisticated electronic controls may include a vehiclecontrol management system 1002, an engine control system 1004, abreaking control system 1006, and a stability control system 1008, eachcapable of automated monitoring and control of one or more aspects of avehicle. As described above, each of these control systems has typicallybeen limited by a lack of timely and accurate tire-to-surface slippageinformation. By integrating one or more of these control systems with anexemplary embodiment of a slippage monitoring control system 800 (seeFIG. 8) that is in communication with one or more slippage monitoringmodules 400 (see FIG. 4) each of the respective control modules may beprovided with accurate tire-to-surface slippage information that therespective vehicle control modules may use to better manage operation ofthe vehicle.

FIG. 11 is a process flow diagram that describes a process that may beused by a vehicle control management system with integrated slippagemonitoring to optimize vehicle performance using tire-to-surfaceslippage information. As shown in FIG. 11, upon startup of a vehicle, atstep S1102, a vehicle control management module may wait, at step S1104,for slippage/alert data from an integrated slippage monitoring controlmodule 800 (see FIG. 8). Upon receipt, at steps 1106, of slippage/alertdata, the vehicle control management module determines, at steps 1108whether tire slippage has been detected. If no slippage has beendetected, processing returns to step S1104 to wait for the next slippagedate update. If slippage is detected, at step S1108, the vehicle controlmanagement module may determine, at step S1110, whether the vehicle isbreaking, and if so, the vehicle control management module may instruct,at step S1112, the breaking control system to take corrective action(e.g., apply anti-lock brake pulsing, etc.). Next, at step S1114, thevehicle control management module may determine whether the vehicle isaccelerating, and if so, the vehicle control management module mayinstruct, at step S1116, the engine control system to take correctiveaction (e.g., reduce power to the wheels, shift gears, etc.). Next, atstep S1118, the vehicle control management module may determine whetherthe vehicle is turning, and if so, the vehicle control management modulemay instruct, at step S1120, the vehicle stability control system totake corrective action (e.g., adjust the vehicle's dynamic suspension,reduce power to the wheels, apply breaks, etc.). Upon turning off thevehicle, at step S1122, the process flow terminates, otherwiseprocessing continues at step S1104 and the vehicle control managementmodule may proceed to wait for further tire-to-surface slippageinformation from the integrated slippage monitoring control module.

It will be appreciated that the exemplary embodiments described aboveand illustrated in the drawings represent are only a few of the manyways of generating and applying tire-to-surface slippage information foruse in improving tire designs and overall vehicle performance. Thepresent invention is not limited to the specific applications disclosedherein, but may be applied to any field that would benefit from accurateand timely tire-to-surface slippage information.

The tire-to-surface slippage monitoring system may be implemented in anynumber of modules and is not limited to the module architecturedescribed above. Each module may be implemented in any number of waysand are not limited in implementation to execute process flows preciselyas described above. The tire-to-surface slippage monitoring systemprocesses described above and illustrated in the flow charts anddiagrams may be modified in any manner that accomplishes the functionsdescribed herein.

It is to be understood that various functions of the tire-to-surfaceslippage monitoring system method and apparatus may be distributed inany manner among any quantity (e.g., one or more) of hardware and/orsoftware modules or units, computer or processing systems or circuitry.

Tire-to-surface slippage monitoring system module(s) may be integratedwithin a stand-alone system or may execute separately and be coupled toany number of external analysis systems and/or vehicle control systemsvia any communications medium (e.g., network, modem, direct connection,etc.). The tire-to-surface slippage monitoring system process can beimplemented by any quantity of devices and/or any quantity of processingsystems, including Application Specific Integrated Circuit (ASIC), FieldProgrammable Gate Array (FPGA), Digital Signal Processor (DSP) orsimilar device to produce tire-to-surface slippage information and tocommunicate between the respective tire-to-surface slippage monitoringsystem modules and/or to communicate with external systems.

It is to be understood that the software of the tire-to-surface slippagemonitoring system process may be implemented in any desired computerlanguage, and could be developed by one of ordinary skill in thecomputer and/or programming arts based on the functional descriptioncontained herein and the flow charts illustrated in the drawings. Forexample, in one exemplary embodiment the tire-to-surface slippagemonitoring system process can be written using the C+ programminglanguage, however, the present invention is not limited to beingimplemented in any specific programming language. The various modulesand data sets may be stored in any quantity or types of file, data ordatabase structures. Moreover, the tire-to-surface slippage monitoringsystem software may be distributed via any suitable medium (e.g., storedon devices such as CD-ROM and diskette, downloaded from the Internet orother network (e.g., via packets and/or carrier signals), downloadedfrom a bulletin board (e.g., via carrier signals), or other conventionaldistribution mechanisms).

The format and structure of internal structures used to holdintermediate information in support of the tire-to-surface slippagemonitoring system process can include any and all structures and fieldsand are not limited to files, arrays, matrices, status and controlbooleans/variables.

The tire-to-surface slippage monitoring system software may be installedand executed on a processing system in any conventional or other manner(e.g., an install program, copying files, entering an execute command,etc.). The functions associated with a the tire-to-surface slippagemonitoring system may be performed on any quantity of processingdevices. Further, the specific functions may be assigned to one or moreof the processing devices in any desired fashion.

The tire-to-surface slippage monitoring system process may accommodateany quantity and any type of data set files and/or databases or otherstructures containing stored data sets, measured data sets and/orresidual data sets in any desired format (e.g., ASCII, plain text, anyword processor or other application format, etc.).

Tire-to-surface slippage monitoring system output can be presented tothe user in any manner using numeric and/or visual presentation formats.Tire-to-surface slippage monitoring system output can be presented asinput to a numerical analysis tool in either numeric or visual form andcan be processed by the numerical analysis tool in any manner and/orusing any number of threshold values and/or rule sets. For example, atechnician can visually interpret tire-to-surface slippage monitoringsystem results via direct inspection of the tire-to-surface slippagemonitoring system numeric output, inspection of a graph or chartdepicting tire-to-surface slippage information and/or via an animatedrecreation of a tire or vehicle slipping based upon the generatedtire-to-surface slippage information.

Further, any references herein to software performing various functionsgenerally refer to computer systems or processors performing thosefunctions under software control. The computer system may alternativelybe implemented by hardware or other processing circuitry. The variousfunctions of the tire-to-surface slippage monitoring system process maybe distributed in any manner among any quantity (e.g., one or more) ofhardware and/or software modules or units, computer or processingsystems or circuitry, where the computer or processing systems may bedisposed locally or remotely of each other and communicate via anysuitable communications medium (e.g., LAN, WAN, Intranet, Internet,hardwire, modem connection, wireless, etc.). The software and/orprocesses described above and illustrated in the flow charts anddiagrams may be modified in any manner that accomplishes the functionsdescribed herein.

The slippage monitoring sensor described above may include any sensorcapable of generating a reference frame and a sample frame and is notlimited to an optical fiber based sensor. For example, exemplaryembodiments of a slippage monitoring sensor may emit any form ofelectromagnetic and/or acoustic energy and may generate reference framesand sample frames based upon the reflected electromagnetic and/oracoustic energy. Such exemplary embodiments would not require an opticalfiber path to the outer surface of the tire, and reduce the mechanicalcomplexity of the sensor. For example, one exemplary embodiment may useradar or sonar based techniques to generate reference frames and sampleframes based upon electromagnetic and/or acoustic energy thatnon-destructively penetrates the tire material.

A reference frame and a sample frame may be any representation of asurface in contact with a portion of the tire footprint contact areathat may be compared in any manner using any technique to determinewhether slippage has occurred. Reference frames and sample frames arenot limited to pixilated images but may include any storable measuredresponse capable of being processed to assess tire-to-surface slippage.

The above exemplary embodiments are exemplary only. The presentinvention should be interpreted to include any implementation of thedescribed capability implemented using any existing, related or futuredeveloped technologies.

From the foregoing description it will be appreciated that the presentinvention includes a novel a method and apparatus for monitoring theperformance of a tire by generating accurate, timely tire-to-surfaceslippage information under any operational/environmental conditions andon any road and/or off-road surface without requiring instrumentation ofthe roadway.

Having described exemplary embodiment of a tire performance surfaceslippage monitoring system, it is believed that other modifications,variations and changes will be suggested to those skilled in the art inview of the teachings set forth herein. It is therefore to be understoodthat all such variations, modifications and changes are believed to fallwithin the scope of the present invention as defined by the appendedclaims. Although specific terms are employed herein, they are used intheir ordinary and accustomed manner only, unless expressly defineddifferently herein, and not for purposes of limitation.

1. A method for determining an amount of wear of a tire tread,comprising: (a) recording a first signal propagation time for a signalto travel along a path that includes a distance from a bottom of a tiregroove to a surface in contact with the tire tread; (b) recording asecond signal propagation time for a signal to travel along a path thatincludes a distance from the bottom of the tire groove to a surface incontact with the tire tread; and (c) determining the amount of wear ofthe tire tread based upon a comparison of the first propagation timewith the second propagation time.
 2. The method of claim 1, wherein (c)further includes: (c.1) subtracting the second signal propagation timefrom the first signal propagation time and dividing the difference bytwo to determine a change in the signal propagation times due to wear ofthe tire tread; and (c.2) determining the amount of wear of the tiretread based upon the determined change in the signal propagation timesdue to wear of the tire tread.